You need to set this is in your web.config, inside <system.net>
section, like this:
<system.net>
<settings>
<httpWebRequest useUnsafeHeaderParsing="true" />
</settings>
</system.net>
If, for some reason, you do not want to do it from your config, you could do it from code by prgrammatically setting your config settings. See this page for an example.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…